1. Field of the Invention
The present invention relates to device and method for JTAG test and especially relates to device and method for JTAG test of a semiconductor device having a JTAG test unsupported terminal at one part thereof.
2. Description of the Related Art
A JTAG (Joint Test Action Group) test is a method of sequentially scanning all external input/output pins of a semiconductor device (integrated circuit), inputting/outputting test data and conducting a test of both an internal function of the semiconductor device and an implemented printed circuit board. Therefore, this test has become a standard specification. The detailed explanation of the JTAG test is described in “Fundamentals and Applications of JTAG Test” (Kazumi Sakamaki, CQ Publication Co.)
Recently, the number of semiconductor devices that support a JTAG test has increased in order to execute a connection test, the debug of a printed circuit board, programs of a writable ROM, etc. when a semiconductor device is mounted on a printed circuit board. However, there are some semiconductor devices in which terminals for inputting/outputting high-speed signals do not support a JTAG test.
FIG. 1A shows such a conventional example. In FIG. 1A, a power source and a GND terminal are abbreviated and boundary scan flip-flops (FF) 2 are inserted into all signal terminals 1 except for a high-speed signal terminal 3. A test access port (TAP) controller 40 for controlling a JTAG test is mounted on a device 100.
FIG. 1B shows a test access port (TAP) that is mounted on a JTAG supported semiconductor device and carries out a JTAG test by externally accessing a circuit block in the semiconductor device. A data register 42 corresponds to a boundary scan FF described in FIG. 1A. The TAP controller 40 described in FIG. 1A includes a TAP control unit 41, a bypass register 43, a command register 44, multiplexers 45 and 46 except for the data register 42 that are all described in FIG. 1B. Terminals include a test data input TDI, a test data output TDO, and a test reset TRST, a test mode selection TMS and a test clock TCK that are control terminals.
The AC characteristic of a terminal of the device 100 is a standard related to data transmission between devices that are not correlated with each other in respect of the production. Since the setup, etc. become further difficult than that in a device if the clock cycles are the same, there is a problem such that the high-speed signal terminal 3 cannot satisfy the AC timing of the terminal 3 if a boundary scan FF is inserted into the terminal 3.
Therefore, the boundary scan FF is inserted into terminals except for a terminal for inputting/outputting a high-speed signal to configure a chain. For example, a terminal for inputting/outputting a high-speed signal includes a memory terminal using an SSTL 2 that is high-speed I/O terminal, etc., a terminal for serially inputting/outputting data, etc. In the case where data are serially input/output, data should be input/output at a rate faster than that of an inner logic.
In the “Fundamentals and Applications of JTAG Test”, a JTAG test method in the case of including a JTAG test unsupported device on a printed circuit board is described. This method is explained in FIG. 2.
If the inner logic of this device is specified although a JTAG test unsupported device 300 is present on a printed circuit board, a JTAG test can be conducted by sandwiching the JTAG test unsupported device 300 with JTAG test supported devices 210 and 220.